1. Field of the Invention
The present invention deals with a method and ultrasonic system for continuous cleaning of solid materials that have a large surface, in the form of sheets or plates, especially flexible materials such as fabrics, plastics, etc.
Ultrasonic energy has been used commercially in industrial cleaning of pieces of rigid materials, especially those that have complex geometries. The cleaning action of high intensity ultrasounds may be mainly attributed to effects related to the phenomenon of acoustic cavitation (formation and implosion of bubbles), such as erosion, agitation and dispersion of the dirt, causing of chemical reactions on the surfaces to be cleaned, penetration of the cleaning solution in pores and cracks, etc.
2. Description of the Related Art
The application of ultrasounds for washing flexible materials and particularly textiles has been tried over the last few years. The strategies have been directed towards the production of cavitation in the entire volume of liquid in which the materials to be cleaned are placed. These systems have not achieved commercial development possibly because they have significant inconveniences. Thus, the use of a large volume of liquid tends to imply a high consumption thereof. On the other hand, it is practically impossible to achieve a homogeneous distribution of the acoustic field in the entire washing volume. This causes a waste of energy (in the areas of low acoustic energy the cavitation threshold is not reached and cleaning does not take place) and causes the washing to be irregular. In order to overcome this situation the washing time must be increased, treatment must be done with a low proportion of material to be washed per volume of liquid and this material must be moved so that it passes through the areas of maximum energy of the washing cavity. Besides, there are other difficulties that come from the gas content in the liquid and from the presence of bubbles between the materials to be washed. In fact, in Spanish patent no. 9401960 good results are only achieved by degassing the liquid so that the concentration of gas is less than 50% of the saturation concentration. Likewise, degassing methods of the washing liquid are proposed in patents EP9320-1142.2 and FR-9304627.
The previous problems have implied practical limitations which, up until now, have hindered the industrial-commercial development of ultrasonic systems for washing of textiles and flexible materials. Nowadays, conventional washing processes in batches that require a significant consumption of water, detergent and energy are used in industrial laundries. Besides the handling system is very elaborate. The continuous washing processes which at times have been tried to be introduced have not been successful due to the low level of cleaning achieved when traditional washing methods have been used.
The process and ultrasonic system that the present invention refers to has some characteristics that manage to solve to a large degree the problems posed by the previous ultrasonic systems, such as the requirement of large volumes of water, the need to agitate the pieces or degassing. At the same time, this process proves to be suitable for continuous treatment thanks to its action being rapid.